The Vos Hestia, operated by Save the Children, rescued more than 100 migrants, most of them from Bangladesh, from a rubber dinghy about 21 miles off the coast of Libya in international waters.

Earlier on Thursday, another non-governmental group, Proactiva Open Arms, said on Twitter that Libyan coastguard officials fired into the air as an act of intimidation while it was rescuing 11 people from a small boat.

No one was injured and the migrants were taken on board the humanitarian vessel. The Libyan coastguard was not immediately available to comment.

Arrivals of migrants to Italy are up almost 18 percent on the same period last year, Italy's Interior Ministry said on Thursday, at more than 65,000.

Since the European Union and Turkey agreed to shut down boat migrants setting off for Greece last year, Italy is Europe's main entry point for refugees and migrants. A record 181,000 migrants arrived on Italy's shores last year.

People smugglers, who operate with impunity in Libya, cram migrants onto unseaworthy boats and send them toward international waters, where humanitarian ships come to their aid. All of Thursday's rescues were performed by NGOs, Italy's coastguard said.

Reporting by Antonio Denti on the Vos Hestia rescue ship; Writing by Steve Scherer in Rome; Editing by Alison Williams